مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3483
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: Sa’d bin 'Ubadah asked the Messenger of Allah (ﷺ) about a vow that his mother had made and she had died before fulfilling it. The Messenger of Allah (ﷺ) said: "Fulfil it on her behalf.”
Musnad Ahmad 3506A saheeh hadeeth]